This invention relates to guillotine dampers and more particularly to the provision of an auxiliary system for providing a gas-tight barrier in flue ductwork. Such a gas-tight barrier is desirable to enable a section of ductwork to be isolated for maintenance purposes without the necessity of a complete shutdown.
Various devices have been disclosed for closing ducts in a fluid type manner. Typical of such devices are gate valve constructions in which a blade is movable to a closed position at which it traverses the duct and is sealed against the duct wall. Devices of this general type are disclosed in British Patent specification Nos: 331,261; 952,265; 1,503,126; and 1,529,234.
The prior art discloses the use of a secondary sealing system in gate valves or guillotine dampers in which a secondary seal is effected after the blade has reached its closed position traversing the duct. British Specification No: 1,529,234 shows such a system, but this has the disadvantage that its operation relies on some flexibility in the wall of the duct when the system is de-actuated to permit movement of the blade. Further, the operating mechanism shown in this prior specification is an integral part of the damper assembly.